If a vertebral body is so severely damaged through disease or injury that it can no longer satisfy its supporting function between the two adjacent vertebral bodies, it can be partially replaced by a known prosthesis (DE-A-4109941, FIG. 8). This prosthesis comprises an upper contact plate for connection to the upper adjacent vertebral body, a lower contact plate for connection to the lower adjacent vertebral body, and, between them, a bridging part which bridges the vertebral body that is to be partially replaced. If the vertebral body to be partially replaced is completely preserved only on the vertebral arch side, a bone cavity is created on its front face and the bridging part is inserted into said bone cavity. For firm connection to the vertebral body to be partially replaced, the bridging part has laterally protruding webs which contain an oblong hole for receiving a securing screw. The securing of the prosthesis on the vertebral body to be partially replaced determines, in addition to the facet articulations, the position of said vertebral body with respect to the adjacent vertebral bodies. Only when its front faces, intended for the securing webs to bear on, are worked in such a way that the vertebra, after connection to the webs, can maintain its natural position defined by the facet articulations, is there any prospect of the prosthesis fitting so exactly that the facet articulations match in exactly the natural manner and no pain caused by movement arises. Such precise working is difficult to achieve in the confined operating site, especially as the position of the prosthesis is influenced not only by the surfaces of the bone cavity, but also by the front face and the screw holes. Inaccuracies in the production of each of these surfaces impair the exactness of the prosthesis position and may therefore lead to pain caused by movement.